Losing your sense of smell can make you fat - and destroy your libido too!
sense of smell is a hugely important but often under-rated tool.
Here the experts reveal how olfaction - our sense of smell - reflects and affects our state of health.
Prone to colds? It could ruin your nose for ever
When we pick up a smell what we are actually detecting are the odour molecules that are released into the air by an object.
As we get older we experience a 'major decline' in our ability to smell things
molecules enter the nose where they bind to hair-like extensions called
cilia; the cilia in turn are attached to smell 'receptors', or nerve
cells, at the top of the nasal passage.
If enough molecules reach a
cell, it fires a signal down the olfactory nerves that run from the nose
to the brain, where the smell is perceived.
As we get older we
experience a 'major decline' in our ability to smell things. This
process may be exacerbated by colds and pollution.
'Every time we
get a bad cold or get close to pollution, a toll is taken, causing
damage to the epithelium (the area of the nasal cavity containing smell
receptors), which can accumulate over time,' says Richard Doty,
professor of otorhinolaryngology and director of the Smell and Taste
Centre at the University of Pennsylvania School of Medicine in the U.S..
People who have more colds may therefore be more likely to have a
poor sense of smell later in life. Half of those aged 65 to 80
experience this 'demonstrable loss' of smell, says Professor Doty, while
for those over the age of 80, three out of four people are affected in
This in turn can have a dramatic effect on sense of taste - 75 per cent of what we perceive to be taste is actually smell, which is why we prefer stronger flavours as we get older.
Women tend to have a more acute sense of smell than men
Women's sense of smell is best
Women tend to have a more acute sense of smell than men - one theory is that hormones play a part.
Indeed, women's sense of smell may be most acute around ovulation, when oestrogen levels are highest.
same fluctuations in smell cycle tend to occur in women on the Pill,
too,' says Professor Doty. Pregnant women also sometimes report a
stronger sense of smell.
There may be an evolutionary reason for
women being better able to detect smell - it could be protective,
explains Tim Jacob, emeritus professor in smell and taste at Cardiff
'When breast-feeding, for example, women need to be very selective about what they eat, and smell is an important part of that,' he says.
One of the functions of our sense of smell is to alert us
to dangers, such as poisonous gases or burning. However, we can adapt to
unpleasant odours over time.
'Take Gorgonzola cheese,' says Professor Jacob. 'It smells very bad and children hate it.
bad smell is bacterial, but it's not actually toxic or hazardous and we
learn to overcome that first impression of disgust or aversion.
'It takes days or years, depending on how often you are exposed to it.'
after a few minutes of being exposed to a strong odour, such as fresh
bread in a bakery, we tend not to notice it until we've left the room
and come back.
Professor Doty explains: 'The brain operates in terms of change and contrast - when there's no contrast, you could say it becomes bored.'
Exercise boosts your receptors
Your sense of smell may be more acute when you exercise.
increases the air flow to the nose because you are breathing more, so
more air flows over the smell receptors, explains Carl Philpott,
honorary consultant ear, nose and throat surgeon at James Paget
University Hospital in Norfolk.
'Some of my patients say they get their smell back temporarily while exercising and then it goes away again.'
may be other times throughout the day that your sense of smell improves
- this is down to our 'nasal cycle', he says. 'One side of the nose is
always more congested - the blood vessels are more engorged - than the
other in order to filter dust particles from the air and warm up the air
you breathe in.
'The other side will be relatively uncongested so
you can breathe properly. Every few hours the process will swap sides so
there will be a point, lasting a few minutes, where they are relatively
Your sense of smell may be slightly improved at this point.
Can't smell? It could be diabetes
Anosmia, the inability to perceive odour, affects around 200,000 Britons, while around 5 per cent of the population is estimated to have problems with their sense of smell. As well as age-related decline, causes include viral infections or a blow to the head, which damage the olfactory nerves.
Damage to the brain through stroke may also cause problems -
and loss of smell can be one of the first signs of neurodegenerative
diseases such as Parkinson's and Alzheimer's, says Professor Doty. These
diseases damage brain cells, which may be important to the sense of
smell. However, those affected may be unaware of their loss of smell.
can have an effect too. As Mark Vanderpump, honorary senior lecturer in
diabetes and endocrinology at the Royal Free London NHS Foundation
Trust, explains: 'Nerve damage is a known long-term complication of
'It happens when the small blood vessels that supply the nerves get damaged in response to chronic high blood sugar.
'Loss of sense of smell appears to be more common in the diabetic population, because of damage to the olfactory nerves.'
your sense of smell can be devastating,' adds Professor Jacob. 'About
17 per cent of people become clinically depressed.'
And weight gain can become a problem.
'Having lost pleasure from eating, some people lose weight, but some actually gain weight because they overcompensate for lack of flavour by eating too many sweet things - you still taste these.'
How smell affects your sex life
Our sense of smell may help determine our choice of partners in the first place, adds Professor Jacob
There is an important link between sex and smell, and some people with anosmia report a loss of libido.
is a form of communication between partners - people respond to the
smell of their partner,' says Mr Philpott. 'A lot of my patients who
lose their sense of smell say they feel a lack of bond with their
Indeed, our sense of smell may help determine our choice of partners in the first place, adds Professor Jacob.
'We're drawn to people who have a different set of immune genes from us - an evolutionary mechanism to encourage us to pass different immune genes to our offspring,' he explains. 'And our own body odour is determined by our immune genes.'
Why cut grass smells so good
Smell is probably the most evocative of all the senses, triggering memories and affecting our mood.
to a recent survey of 2,000 adults, freshly mown grass, pencil shavings
and baby powder are the aromas most likely to send Britons harking back
to the past.
'Interestingly, sense of smell is subconscious,' explains Professor Jacob. This is because it affects our limbic system, the primitive part of the brain where emotions are stored.
of smell was illustrated by a German study in 2008, which found that
people exposed to the smell of roses during sleep had pleasant dreams,
while those exposed to rotten egg odour had unpleasant ones.
'Smell is the only sense which doesn't switch off when we sleep,' adds Professor Jacob.
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